According to the Regulation on statistical units an activity must be regarded as ancillary if it satisfies all the following conditions:

- it serves only the unit referred to: in other words, goods or services produced must not be sold on the market;- a comparable activity on a similar scale is performed in similar production units;- it produces services or, in exceptional cases, non-durable goods which do not from part of the unit's end product (e.g. small implements or scaffolding);- it contributes to the current costs of the unit itself, i.e. does not generate gross fixed capital formation.

Context:

It should be noted that under the above definition the following are not to be regarded as ancillary activities:

- production of goods or work carried out which forms part of fixed capital formation: in particular, construction work for own account. This is in line with the method used in NACE Rev. 1, where units carrying out construction work for own account are classified under the building industry if data are available;- production, a significant part of which is sold commercially, even if much is used as consumption in connection with the principal activity or secondary activities;- the production of goods which subsequently become an integral part of the output of the principal or secondary activity - e.g. production of boxes, containers, etc. by a department of an enterprise for use in packing its products;- the production of energy (integrated power station or integrated coking plant), even where this is consumed in its entirety in the principal or secondary activity of the parent unit;- the purchase of goods for resale in (an) unaltered state;- research and development.

These activities are not very widespread and do not produce services which are used in current production.

Source
Publication:

Council Regulation (EEC), No. 696/93, Section IV B1 and B4 of 15.03.1993 on the statistical units for the observation and analysis of the production system in the Community.